We tried to think of new, exciting things that Enhancements could bring to the game. We determined that adding mini-powers to your existing ones had a lot of potential, as the sky would nearly be the limit on what we could accomplish with these new Enhancements. In addition we wanted Enhancements that never expired, because nothing was worse than leveling up in a mission to a point where the majority of your Enhancements turned red (useless), and instead of that level-up making you more powerful, it actually made you less.

Via MMORPG